In the printing technology, different methods and apparatuses for transporting a sheet in a printing machine are known. DE 10113885 A1, corresponding to U.S. Pat. No. 6,993,278, for example shows a transport apparatus having a circulating transport belt, which is air-permeable, in order to allow sucking sheets via negative pressure to the transport belt. The force with which a respective sheet is adhered to the transport belt depends on the permeability of the suction belt, as for example defined by the size and the amount of through openings there through, as well as the amount of negative pressure applied. Inasmuch as the number and the size of the through openings should usually be kept small, in order to avoid influencing processes, which may act on the sheet being transported, a sufficient holding force may not be provided in all cases.
In DE 10319846 A1, corresponding to U.S. Pat. No. 6,745,001, an alternative transport apparatus having a circulating transport belt is described. In this transport apparatus the transport belt is electro-statically charged via a corona facing the transport belt, in order to adhere a sheet on that transport belt by electro-static forces. In those areas, in which a sheet contacts a thus electro-statically charged transport belt, a large holding force is provided. If the sheet, however, is not flat on the transport belt, when that charge is applied, the holding force only acts in the contact areas. If the sheet lies on the transport belt in a bowed manner, the electro-static forces acting in the contact areas would hold the sheet during the transportation in this bowed manner. This could substantially influence any process to be performed on the sheet during the transportation, such as for example printing an image on the sheet.